1. Field of the Invention
The present invention relates to floating tap holders, and more particularly pertains to a new and improved floating tap holder which provides a precise alignment of a tap with the center line of a previously drilled hole and also provides a constant axial feed force to the tap. The standard practice for tapping threads in a predrilled hole in a work piece is to use a combination of vertical and rotating hand pressure, while trying to keep as perfect a vertical alignment as possible between the predrilled hole center line and the hand tap. It is also a common practice to reverse the tap rotation one fourth turn for every three fourths turn of tap advance, in order to break the metal chip generated by the tapping operation. This hand tapping method misaligns the tap center line with the predrilled hole center line, causing tap breakage and destroying an expensive work piece such as a tool fixture, die fixture or an expensive machined assembly.
2. Description of the Prior Art
Various types of floating tap holders are known in the prior art. A typical example of such a floating tap holder is to be found in U.S. Pat. No. 4,050,842, which issued to A. Janin on Sept. 27, 1977. This patent discloses a floating spring biased tap holder. No provision, however, is made for a hand actuated drive of the tap. The device includes a rotary cutting tool and a quick change tool holder operative to support the tool in a floating engagement and permitting the tool to shift transversely of the holder through a limited distance. The tool support has a cylindrical holder having a transverse T-slot cut therethrough and shaped to receive a T-shaped tongue portion formed on the tap shank. A sleeve has a bore which is in a snug sliding fit on the cylindrical holder and has a spring normally maintaining the sleeve surrounding the cylindrical holder and surrounding a portion of the length of the shank between the tongue and the cutting edges. Various other floating tool constructions are known in the art. U.S. Pat. No. 3,550,229, which isued to C. Zenses on Dec. 29, 1970, discloses a rasp having a spring biased floating center. U.S. Pat. No. 2,195,645, which issued to E. Gairing on April 2, 1940, discloses a floating pilot bar assembly for a thread chaser. This device is utilized in chasing threads on internal diameter portions of work pieces. U.S. Pat. No. 2,188,584, which issued to J. Tyne on Jan. 30, 1940, discloses a pipe end reamer having a pilot guide bar. U.S. Pat. No. 1,041,675, which issued to H. Robinson on Oct. 15, 1912, discloses a combined reamer and tap. A spring biased floating reamer is secured to a cylindrical flange which is mounted on a conventional tap by a set screw.
Various torque limiting free floating tapping spindles are also disclosed by the prior art. These tapping spindles are designed for use in high production automated transfer line machining operations, and are not suitable or cost effective for use in hand tapping operations.
While the above mentioned devices are suited for their intended usage, none of these devices provides a floating tap holder which utilizes a hand drive rod and insures the alignment of the tap with the center line of a previously drilled hole. Also, none of the above mentioned devices provide for a constant axial feed force on a tap. Further, none of the aforesaid devices provide a floating tap holder which utilizes the chuck of a conventional machine tool such as a drill press, milling machine or lathe to align the tap with the center line of a previously drilled hole, and at the same time allows a hand rotary feed of the tap. Inasmuch as the art is relatively crowded with respect to these various types of floating tap holders, it can be appreciated that there is a continuing need for and interest in improvements to such floating tap holders, and in this respect, the present invention addresses this need and interest.